Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations in a fuel system canister. During subsequent engine operation, the fuel vapors are purged to the engine with the purging carefully controlled so as to meet stringent federal emissions regulations.
The inventors herein have recognized that fuel vapor management, including the recovering and disposing of fuel vapors, can add substantial cost and complexity to a vehicle's fuel system. For example, in hybrid vehicles where the reduced frequency of engine operation prolongs the duration between purging opportunities, the use of a sealed steel tank or a bladder tank that can store a large amount of fuel vapors can add substantial costs. As another example, a hybrid vehicle's fuel economy may be affected if the engine has to be operated to enable the stored vapors to be ingested into the engine.
Thus in one example, some of the above issues may be at least partially addressed by a method for a vehicle fuel system, comprising floating a layer of gel-foam fire retardant on a surface of liquid fuel in a fuel tank to reduce an amount of fuel vapors generated in a dome region of the fuel tank, the vehicle being an on-road vehicle. In this way, fuel vapor generation can be reduced at a low cost.
In one example, a vehicle fuel system may include a fuel tank for delivering fuel to engine cylinders. The fuel tank may include a fuel pump coupled therein. A layer of gel-foam fire retardant may be layered on the fuel such that the layer floats on the surface of the liquid fuel. The layer may be a single continuous layer and may remain in place throughout the life of the vehicle, with replacements performed only as necessary. By positioning the layer on the fuel surface, fuel vapor generation (e.g., diurnal losses) may be reduced. Control of the fuel pump may be tied to a position of the layer within the fuel tank so as to enable the pump to be shut off before any of the gel-foam fire retardant is ingested into a fuel pump inlet. In addition, a bottom of the fuel tank may be modified with a depression for housing the fuel pump. For example, the layer of gel-foam fire retardant may be coupled to a fuel level sensor (such as a fuel level sensing arm with a float) that monitors a position of the layer in the fuel tank relative to a threshold position, wherein the threshold position is based on a road incline, vehicle rate of acceleration/deceleration, rate of vehicle lateral acceleration (e.g., turning,), steering wheel angle, yaw, etc. As such, changes to any of these parameters may affect a position of the gel-foam fire retardant relative to a location of the fuel pump inlet. Thus, by enabling pump operation only if the layer is sufficiently distant from the threshold position and by disabling the pump in response to the layer being sufficiently close to the threshold position, ingestion of gel-foam fire retardant in the fuel pump is obviated.
In this way, a simple and cost effective solution is provided for reducing evaporative emissions. By layering a gel-foam fire retardant on the surface of fuel in a fuel tank coupled to an on-road vehicle, the evaporative emissions benefits of a bladder tank can be achieved for a fraction of the cost of a bladder tank. In addition, the use of a gel-foam fire retardant in the layer allows unwanted fuel vaporization to be reduced in the event of tank degradation (e.g., tank rupture). By adjusting fuel pump operation based on the position of the layer within the fuel tank, ingestion of the gel-foam fire retardant into the fuel pump can be reduced. By reducing evaporative emissions, vapor purging frequency is reduced, and fuel economy penalties incurred during the purging of fuel vapors, particularly in a hybrid vehicle, can be reduced.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.